Matrice 4E RTK height issue

[Iain]

Hi all,
I have recently flown a survey mission with our Matrice 4E. But when I try to add GCP's to the job there is a 47M error between the drone data height and the GCP height I know the GCP's are correct.

The RTK height says it's at 0 this doesn't seem correct to me but I've never noticed it before and it's been fine on previous jobs before this last one which was just after a firmware update.
Any ideas on how to fix this would be appreciated.

 

[Iain]

Photo of connected RTK for conformation of the 0M height issue

 

[Dave Pitman]

Looking up the coordinate being reported for the base, it's elevation should be around 58m, not 0.

 

[Iain]

Looking up the coordinate being reported for the base, it's elevation should be around 58m, not 0.

Thanks for the reply.

That's my issue I have GPS data for the same area which I know is correct at around the 58m mark but my drone data says it's between 10-11m in height when it's run off in Terra I have never had this issue before and other than a firmware update the day before the flight nothing has changed.

So I'm at a loss as to what's happening

 

[Dave Pitman]

What is the source of the NTRIP data?

 

[Iain]

What is the source of the NTRIP data?

VRS Network subscription the same one used on the GPS data which is fine.

 

[Dave Pitman]

Do the height values in the image meta data match reality?

 

[Iain]

Forgive my ignorance but how do you check that

 

[Dave Pitman]

There are many free apps to view image exif data. But, for simplicity's sake, if you are on windows, you can right click on the image and select PROPERTIES > DETAILS (maybe similar on mac)

Scroll down to the GPS section and it displays the altitude. This should roughly correspond to the ground elevation at your flight location + the altitude of the drone.

 

[Iain]

Yes that seems to be roughly correct

 

[Dave Pitman]

If your GCP heights are correct, and the height of your image exif seems correct, then you should be good.

So, what exactly do you mean when you say "there is a 47M error between the drone data height and the GCP height"?

When the drone is at mission height, it should be different than the GCP height which is on the ground?

 

[Iain]

So when I have ran off the drone data and processed it to OSGB 36 it should be around 57m In level but it's coming out at 10-11m in level hence the 47m average error in real life ground levels and what the drone data is producing.

So it wouldn't find the GCP'S to fit too as they are higher than the drone flight data.

 

[Dave Pitman]

Sorry, I'm not following your terminology. I suspect you have something set up incorrectly in your processing. If you want to share a partial set of the images and a .csv with your ground control, I'd be happy to take a look at it.

 

[Iain]

So I loaded the photos into DJI Terra processed them into OSGB 36 output and then added my GCP's which I located via GPS and the GCP heights are 57m ground OS levels and the drone data is coming out at 10m ground in the same coordinate system.

I'll be happy to share a small sample if that's easier

 

[Dave Pitman]

I don't use Terra, so no help there. But if you just take the fact that your ground shots are good, and the altitude written to the images are good, then, the only place for a great amount of error added has to come from the processing inputs.

You're not mixing up feet and meters on anything, correct?

Have you tried processing and not applying any CS transformation?

What is the CS used by your NTRIP provider?

If you have Dropbox or equiv., load up some images.

 

[Iain]

Thanks for your assistance so far.
VRS RTK is on OSGB 36 CS

I will upload some photos tomorrow see if that can help